Karakin [l,2,6-tri(3-nitropropanoyl)-β-D-glucopyranose], derived from the roots ofLotus pedunculatus, was administered to third-instar larvae ofCostelytra zealandicaby oral injection. Within 10 min, karakin itself could no longer be detected. Nitro compounds recovered from body extracts, amounting to only 20% of the amount injected, were present as free 3-nitropropionic acid and associated with a dichloromethane/ethanol insoluble fraction. Rapid hydrolysis of karakin was also shown by homogenates of larval gut fractions: the hydrolytic activity was largely enzymic and was localised predominantly in the first half of the rudimentary gut of the grass grub.